'Chattooga', found near the Chattooga River which forms the boundary between South Carolina and Georgia, is a natural hybrid of Rhododendron calendulaceum. 'Chattooga' is both seed and pollen fertile.

Audra State Park in West Virginia also contains natural hybrids of Rhododendron calendulaceum. Such natural hybrids occur when tetraploid and diploid deciduous azalea species, blooming at the same time, coexist.